If you are writing to supporters of gay marriage, this is a perfectly reasonable premise. However, if your goal is to persuade the 46% of people who oppose same-sex marriage to change their view, this is a terrible premise. They will find this statement unreasonable, and they will stop reading.

Result? Your article fails. You can't persuade a reader who won't read past the first sentence.

Instead, begin with a premise such a reader will accept:

All Americans should have equal rights under the law.

A statement like this resonates with everyone, and you can gradually work from this premise to a persuasive conclusion supporting same-sex marriage.

If your goal is to reach readers who don't agree with you, you've got to start on common ground and then persuade them to come around to your view.

Don't mow your readers down. Back off on your premise and draw your readers in. Then you'll have a better shot at persuading them.